This invention relates in general to universal joints for use in vehicular drive train assemblies. In particular, this invention relates to an improved structure for a half round end yoke and a pair of retainer straps for retaining an opposed pair of bearing cups to the half round end yoke in such a universal joint.
In most land vehicles in use today, a drive train system is provided for transmitting power from a source of rotational power, such as an internal combustion or diesel engine, to a plurality of driven wheels of the vehicle. A typical drive train system includes a clutch, a transmission, a driveshaft assembly, and an axle assembly that are connected in series between the engine and the driven wheels of the vehicle. The clutch is connected to the output shaft of the engine for selectively providing a driving connection therethrough to the input shaft of the transmission. The transmission provides a plurality of gear ratios between the input shaft and an output shaft connected to the forward end of the driveshaft assembly. The driveshaft assembly is elongated so as to transmit the rotational power from the transmission to the vicinity of the driven wheels of the vehicle. The axle assembly includes an input shaft that is connected to the rearward end of the driveshaft assembly, a differential gear mechanism that is rotatably driven by the input shaft, and a pair of output axle shafts that connect the differential gear mechanism to the driven wheels of the vehicle.
Usually, the output shaft of the transmission and the input shaft of the axle assembly are not co-axially aligned with one another. To accommodate this, a typical driveshaft assembly includes an elongated driveshaft tube having a pair of universal joints secured to the ends thereof. The first universal joint is connected to the output shaft of the transmission, while the second universal joint is connected to the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the transmission through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment therebetween.
A typical universal joint includes a cross having a central body portion with four trunnions extending outwardly therefrom. The trunnions are oriented in a single plane and extend at right angles relative to one another. A bearing cup is mounted on the end of each of the trunnions. Needle bearings or similar means are provided between each of the trunnions and its associated bearing cup to permit the bearing cup to rotate relative to the trunnion. A first pair of opposed bearing cups is connected to a first end yoke, while a second pair of opposed bearing cups is connected to a second end yoke.
Typically, the first and second end yokes can be classified as one of two general structures, namely, a full round end yoke and a half round end yoke. A full round end yoke includes a pair of opposed arms having respective cylindrical openings formed therethrough, within which the opposed bearing cups are inserted. Flat retaining members are usually provided over the outer ends of the bearing cups for retaining them within the cylindrical openings. A half round end yoke includes a pair of opposed arms having respective semi-cylindrical recesses formed therein, within which the opposed bearing cups are received. Retaining straps are usually provided about the circumferential sides of the bearing cups for retaining them within the semi-cylindrical recesses.
A typical structure for a retaining strap for use with a half round end yoke includes a stamped plate having a curved central portion with a pair of straight end portions extending outwardly therefrom. The curved central portion of the retainer strap is semi-cylindrical in shape so as to conform with the outer surface of the bearing cup. The end portions of the retainer strap have respective holes formed therethrough that can be aligned with threaded bores formed in the arms of the half round end yoke. Threaded bolts or similar fasteners extend through the holes formed through the end portions of the retainer strap into cooperation with the threaded bores formed in the arms of the half round end yoke so as to secure the retainer strap thereto. In this manner, the bearing cup is retained within the semi-cylindrical recess of the half round end yoke by the retainer strap.
Typically, the holes formed through the end portions of the retainer straps and the threaded bores formed in the arms of the half round end yoke have been oriented in a direction that extends parallel to, but is offset from, the axis of rotation of the half round end yoke. Thus, the threaded bolts or similar fasteners were installed and removed by engaging them with a tool that was also oriented in a direction that extended parallel to, but offset from, the axis of rotation of the half round end yoke. This half round end yoke retaining structure has functioned satisfactorily for many years with conventional driveshaft tubes.
Traditionally, driveshaft tubes have been formed from steel alloys having a constant diameter throughout the entire length thereof. Steel alloys are relatively high strength materials. Thus, for a given torque load requirement in a vehicle, a steel alloy driveshaft tube can be formed having a relatively small diameter. For example, in many light trucks and similar vehicles, conventional steel alloy driveshaft tubes have been formed having a diameter of approximately three to three and one-half inches. Unfortunately, steel alloys are also relatively heavy materials. As mentioned above, the weight of the driveshaft assembly is supported at its forward end by the output shaft of the transmission and at its rearward end by the input shaft of the axle assembly. Thus, care must be taken to insure that the weight of the driveshaft assembly can be adequately supported by the transmission bearings that rotatably support the output shaft of the transmission and the axle bearings that rotatably support the input shaft of the axle assembly.
In some vehicles, the distance between the output shaft of the transmission and the input shaft of the axle assembly is relatively small. In those vehicles, the weight of a single elongated driveshaft tube formed from a steel alloy material can be adequately carried by the transmission and axle bearings. However, in other vehicles, the distance between the output shaft of the transmission and the input shaft of the axle is relatively large. It has been found that the weight of a single elongated driveshaft tube formed from a steel alloy material places an undesirably large load on the transmission and axle bearings. In those instances, it is known to split a single elongated driveshaft tube formed from a steel alloy material into a pair of relatively short driveshaft tube sections that are themselves connected together by a third universal joint. A center bearing assembly is provided to support the weight of the interior ends of the two driveshaft sections on the frame of the vehicle, while allowing relative rotation thereof. This structure has been found to sufficiently reduce the amount of weight placed upon the transmission and axle bearings to an acceptable level. However, this structure adds undesirable cost and complexity to the structure and installation of the driveshaft assembly.
Recently, there has been a movement to form driveshaft tubes from alloys of aluminum, as opposed to steel. Aluminum alloys are both strong and lightweight and, therefore, are usually regarding as desirable substitutes for steel alloys in driveshaft tubes. Thus, the weight of a single elongated driveshaft tube formed from an aluminum alloy material is much lighter that a comparably sized driveshaft tube formed from a steel alloy material. Accordingly, a single elongated driveshaft tube formed from an aluminum alloy material can be used in lieu of a split driveshaft assembly structure formed from a steel alloy material (including the third universal joint and center bearing assembly discussed above) without placing an undesirably large load on the transmission and axle bearings.
However, it has been found that an aluminum alloy driveshaft tube having a diameter that is comparable to the diameter of a corresponding steel alloy driveshaft tube tends to vibrate when the vehicle is driven at normal operating speeds. Such vibrations are undesirable because they generate noise. To address this, it has been found desirable to form aluminum alloy driveshaft tubes having a diameter that is somewhat larger than the diameter of a corresponding conventional steel driveshaft tube. For example, in a vehicle drive train system including a steel alloy driveshaft tube having a diameter of approximately three to three and one-half inches, it has been found acceptable to substitute an aluminum alloy driveshaft tube having a diameter of approximately five inches. The larger diameter aluminum alloy driveshaft tube does not vibrate when the vehicle is driven at normal operating speeds. Unfortunately, it has been found that the use of a larger diameter driveshaft tube can undesirably restrict access of the tool to engage the threaded fasteners for installation of the driveshaft assembly onto the vehicle. Thus, it would be desirable to provide an improved structure for a half round end yoke and a pair of retainer straps that facilitates the use of a tool for installing and removing the threaded fasteners when the universal joint is used in conjunction with a driveshaft tube having a relatively large diameter.